JP4461172B2 - Foam molded body having voids - Google Patents

Description

  The present invention relates to a foamed molded article having voids. More specifically, the present invention relates to a foamed molded article having a void having excellent heat resistance, light weight and sound absorption, and having significantly improved chemical resistance and bending strength. The foamed molded product of the present invention is particularly required to have sound absorbing performance. For example, a ceiling material, a side impact pad that protects an occupant in the event of a vehicle collision, a lower limb energy absorbing material (tibia pad), an automobile interior material represented by a floor spacer, Also, it can be suitably used as automobile members such as bumpers and construction members such as wall materials and floor materials.

  In general, a foam of a polyethylene resin is used as a packaging material because it has high elasticity and excellent impact resistance. However, it has disadvantages such as low rigidity and low compressive strength. On the other hand, styrene resin foams are excellent in rigidity but have the disadvantage of being brittle.

  As methods for improving such defects, Japanese Patent Publication No. 51-46138 (Patent Document 1), Japanese Patent Publication No. 52-10150 (Patent Document 2), Japanese Patent Publication No. 58-53003 (Patent Document 3), Japanese Laid-Open Patent Publication No. 62-59642 (Patent Document 4) proposes a method in which a polyethylene resin is impregnated with a styrene monomer and polymerized to obtain styrene-modified polyethylene resin expanded particles.

Moreover, as a foaming molding obtained by heat-foaming a styrene-modified polyethylene resin foam piece in a mold and fusing the pieces together, the pieces have a gap of 10 to 40% between the pieces. A fused styrene-modified polyolefin resin foam molded article is described in JP-A-7-80873 (Patent Document 5).
Japanese Patent Publication No.51-46138 Japanese Patent Publication No.52-10150 Japanese Patent Publication No.58-53003 JP-A-62-59642 Japanese Patent Laid-Open No. 7-80873

  In the method described in Japanese Patent Publication No. 51-46138, etc., since the inorganic nucleating agent is not used in the polyethylene resin, the obtained modified resin particles are contained in the polyethylene resin particularly near the surface portion thereof. It is difficult to disperse styrenic resin in the form of particles, and it tends to be unable to exhibit sufficient chemical resistance. Furthermore, even when an inorganic nucleating agent is used for the polyethylene resin, since the polymerization of the styrene monomer is usually performed at around 90 ° C., the styrene resin dispersed in the polyethylene resin near the surface exceeds 1 μm. Such a large particle tends to be dispersed and cannot exhibit sufficient chemical resistance.

In addition, the foamed molded article described in JP-A-7-80873 can obtain a desired porosity as well as a compressive strength that can sufficiently withstand the use as a culvert drainage material. Has been. A foamed molded article having such a porosity can also exhibit good sound absorption performance.
However, since the present inventors are a foam-molded article having a desired porosity, for example, the strength such as bending strength is insufficient for use as an industrial member such as an automobile interior material. I knew I couldn't stand it.

The present invention has been made to solve the problems described above, to provide such desired to provide a porosity to exhibit good sound absorbing performance, and a high flexural strength can also exhibit foam molded article With the goal.
Thus, according to the present invention, 50 to 800 parts by weight of a styrenic resin per 100 parts by weight of a non-crosslinked linear low density polyethylene resin that can be obtained using a metallocene catalyst containing an inorganic nucleating agent. A styrene-modified resin containing a styrene resin dispersed in the form of particles in the surface layer part from the particle surface to at least 5 μm and the central part from the particle center to the radius of 5 μm. It is obtained by pre-expanding expandable particles obtained by impregnating a linear low density polyethylene resin particle with a volatile foaming agent, and foaming the resulting pre-expanded particles, and has a porosity of 5 to 50%. A foamed molded article is provided.

  The foamed molded product of the present invention is a foamed molded product obtained from styrene-modified polyethylene resin particles having the following configuration. That is, first, among non-crosslinked and linear low-density polyethylene resins, non-crosslinked and linear low-density polyethylene resins that can be obtained using a metallocene catalyst are used. Furthermore, it is a resin particle modified so as to contain 50 to 800 parts by weight of a styrene resin with respect to 100 parts by weight of the polyethylene resin containing an inorganic nucleating agent, and this modified resin particle is from the particle surface to 5 μm. In the surface layer portion and the central portion from the particle central portion to the radius of 5 μm, the styrenic resin is dispersed in a submicron size in a particle shape of 0.8 μm or less. Therefore, the polyethylene resin layer is formed on the particle surface.

  Thus, since the linear low density polyethylene-type resin layer which can be obtained using a metallocene catalyst is formed in the particle | grain surface part, the chemical resistance of a foaming molding can be improved. In addition, since the styrene resin can be dispersed into submicron particles in the central part from the particle central part to the radius of 5 μm, even a foamed molded article having a desired porosity can be melted. The wearing strength can be increased and the strength properties can be improved. Further, it is possible to obtain a foamed molded article having an extremely high bending strength that could not be exhibited by linear low density polyethylene resin particles polymerized with a Ziegler-Natta catalyst.

(Brief description of the drawings)
FIG. 1 is a TEM photograph of a cross section of a surface layer portion of a modified resin particle of Example 1 according to the present invention.
FIG. 2 is a TEM photograph of a cross-section at the center of the modified resin particle of Example 1 according to the present invention.
FIG. 3 is a TEM photograph of a cross section of the surface layer portion of the modified resin particle of Example 2 according to the present invention.
FIG. 4 is a TEM photograph of a cross-section at the center of the modified resin particle of Example 2 according to the present invention.
FIG. 5 is a diagram obtained by tracing the TEM photograph of FIG.
6 is a TEM photograph of a cross section of the surface layer portion of the modified resin particle of Comparative Example 1. FIG.
FIG. 7 is a TEM photograph of a cross-section at the center of the modified resin particle of Comparative Example 1.
FIG. 8 is a TEM photograph of the cross section of the surface layer of the modified resin particle of Comparative Example 2.
FIG. 9 is a TEM photograph of a cross-section at the center of the modified resin particle of Comparative Example 2.
FIG. 10 is a TEM photograph of the cross section of the surface layer portion of the modified resin particle of Comparative Example 9.
FIG. 11 is a TEM photograph of a cross-section at the center of the modified resin particle of Comparative Example 9.
FIG. 12 is a schematic view of a foam molding machine that can be used in the present invention.

(Explanation of symbols)
1a Cavity 2 Female mold 2a, 3a Steam chamber 2b, 3b Steam ejection slit hole 2c, 3c Steam supply pipe 2d, 3d Steam discharge pipe 3 Male mold 4 Steam controller 5 Drain valve 6 Pre-foamed particle 7 Filler 9 Pressure sensing device 10 control means

The foamed molded article of the present invention is obtained by pre-foaming expandable particles obtained by impregnating styrene-modified polyethylene resin particles (hereinafter referred to as modified resin particles) with a volatile foaming agent, and foaming the resulting pre-foamed particles. It is obtained by molding and has a porosity of 5 to 50%.
The modified resin particles are based on 100 parts by weight of a non-crosslinked linear low density polyethylene resin (hereinafter simply referred to as polyethylene resin) that can be obtained using a metallocene catalyst containing an inorganic nucleating agent. 50 to 800 parts by weight of styrene resin is contained, and the surface layer part from the particle surface to at least 5 μm and the center part from the particle center part to the radius of 5 μm are dispersed with a particulate styrene resin of 0.8 μm or less. Yes.

First, the modified resin particles and pre-expanded particles for producing a foamed molded product will be described.
Examples of the metallocene catalyst include known metallocene catalysts used for the polymerization of ethylene monomers. For example, a metallocene catalyst containing a tetravalent transition metal element can be suitably used. More specifically, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-t- Butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-t-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium chloride, methylphenylsilyltetramethylcyclopentadienyl- t-Butylamide Hafnium Dichloride, Indenyl Titanium Tris (Dimethylamide), Indenyl Titanium Tris (Diethylamide), Indenyl Titanium Tris Di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like. These metallocene catalysts containing a tetravalent transition metal may be used alone or in combination of two or more. Moreover, you may use together with cocatalysts, such as a methylaluminoxane and a boron type compound, for example.

Moreover, as a polyethylene-type resin, the homopolymer of ethylene, the copolymer of ethylene and an alpha olefin, etc. are mentioned.
As α-olefins, propylene, 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-heptene , 1-octene and the like. Of these, 1-butene and 1-hexene are preferable. These α-olefins may be used alone or in combination of two or more.

The constitutional ratio of ethylene and α-olefin may be appropriately changed according to desired physical properties, but is preferably in the range of 1: 0.01 to 0.1 (weight ratio). Note that low density means a range of about 0.910 to 0.925 g / ml.
The polymerization method of the polyethylene resin uses a metallocene catalyst. For example, in the case of an ethylene homopolymer, a gas phase polymerization method can be used. In the case of a copolymer of ethylene and an α-olefin, an inert medium is used. Examples thereof include a solution polymerization method, a bulk polymerization method substantially free of an inert medium, and a gas phase polymerization method.

The polyethylene resin preferably has a molecular weight distribution (Mw / Mn) of 1.5 to 3.5 as measured by GPC (gel permeation chromatography). In the case of this molecular weight distribution range, there is an effect that molding is easy and the strength (particularly bending strength) of the obtained molded body can be improved.
Non-crosslinked, linear polyethylene resins polymerized using a metallocene catalyst include: FMRN series from Nihon Unicar, Evolue F series from Sumitomo Chemical, Evolue series from Mitsui Chemicals, Dow Chemical Affinity PL series manufactured by the company and the like can be mentioned.

Moreover, you may use together another polymer or copolymer in the range which does not inhibit the effect made into the objective of this invention. Specific examples thereof include crosslinked and / or branched low density polyethylene, high density polyethylene, ethylene / propylene copolymer, ethylene / vinyl acetate copolymer or ethylene acrylic acid copolymer, and two or more of these Combinations are listed.
As the inorganic nucleating agent, for example, talc, silicon dioxide, mica, clay, zeolite, calcium carbonate and the like can be used.

  The amount of the inorganic nucleating agent used is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1.5 parts by weight, per 100 parts by weight of the polyethylene resin particles. If it is less than 0.1 part by weight, it is difficult to disperse a styrene resin of 0.8 μm or less in a polyethylene resin in the form of particles, which is not preferable. If it exceeds 2 parts by weight, the strength of the foamed molded product tends to decrease, such being undesirable.

Furthermore, additives such as a colorant, a flame retardant, an antioxidant, and an ultraviolet absorber may be contained in the polyethylene resin particles as necessary.
Among these, as the colorant, both inorganic and organic colorants can be used. In particular, inorganic colorants such as iron oxide and carbon black are preferred.

Examples of the iron oxide include α-FeOOH (hydrous crystal) as a yellow type, α-Fe ₂ O ₃ as a red type, and (FeO) x (Fe ₂ O ₃ ) y as a black type. . In these iron oxides, part of Fe may be replaced with other metals such as Zn and Mg. Further, these iron oxides may be mixed and used in order to obtain a desired color. Among them, the black line _{(FeO) x (Fe 2 O} 3) is preferably Fe ₃ O ₄ contained to y.
The iron oxide preferably has an average particle size of 0.1 to 1 μm, and more preferably 0.2 to 0.8 μm. The average particle size can be measured with a laser diffraction particle size distribution meter (Rodos manufactured by JEOL Ltd.).

  The iron oxide is preferably contained in the range of 1.5 to 70% by weight in the polyethylene resin particles, more preferably in the range of 5 to 40% by weight, and still more preferably in the range of 10 to 30% by weight. If it is less than 1.5% by weight, the polyethylene resin particles may not be sufficiently colored, which is not preferable. When it is more than 70% by weight, it is difficult to mix in the polyethylene resin particles, and since the specific gravity of iron oxide is larger than that of the polyethylene resin, the polyethylene resin particles become heavy and uniformly impregnate the styrene monomer. It is not preferable because it is difficult.

Examples of carbon black include furnace black, channel black, thermal black, acetylene black, graphite, and carbon fiber.
Carbon black is preferably contained in the range of 1 to 50% by weight in the polyethylene resin particles, and more preferably in the range of 2 to 30% by weight. If it is less than 1% by weight, the polyethylene resin particles may not be sufficiently colored, which is not preferable. When it is more than 50% by weight, it is not preferable because it is difficult to mix in the polyethylene resin particles.

Examples of the styrene resin include resins derived from monomers such as styrene, α-methylstyrene, vinyltoluene, and chlorostyrene.
The amount of the styrenic resin is 50 to 800 parts by weight, preferably 100 to 700 parts by weight, per 100 parts by weight of the polyethylene resin. If it is less than 50 parts by weight, the property that the rigidity of the styrene-based resin is good is hardly exhibited. Moreover, when it exceeds 800 weight part, the elasticity of polyethylene-type resin is high, and the characteristic that oil resistance and impact resistance are favorable is hard to express. Furthermore, the styrene monomer is not sufficiently absorbed in the polyethylene resin, and a polymer powder is produced in which the styrene monomer itself is polymerized alone.

In the case of expandable particles, if the amount of the styrene resin is less than 50 parts by weight, the retention of the volatile foaming agent becomes extremely poor, so that it is difficult to reduce the density and the foam moldability is poor. .
In particular, it is difficult to obtain modified resin particles and expandable particles in which the amount of the styrene resin is 300 parts by weight or more, and the modified resin particles and expandable particles that uniformly contain the styrene resin by the conventional method. However, in the present invention, it can be obtained.

The pre-expanded particles are obtained by impregnating the modified resin particles with a volatile foaming agent to form expandable particles, and foaming the expandable particles.
As the volatile blowing agent, for example, hydrocarbons such as propane, n-butane, isobutane, pentane, isopentane, cyclopentane, hexane and the like can be used alone or in admixture of two or more.
The content of the volatile foaming agent is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the resin (the total of polyethylene resin and styrene resin) constituting the foamable particles.

The modified resin particles and the expandable particles are cylindrical, substantially spherical or spherical with L / D of 0.6 to 1.6, where L is the particle length and D is the average diameter. The diameter is preferably 0.3 to 3.0 mm.
When L / D is smaller than 0.6 or larger than 1.6, that is, the flatness is large, pre-expanded particles obtained from the modified resin particles and the expandable particles are filled into a mold and the expanded molded body When obtaining the above, the filling property into the mold is liable to deteriorate, which is not preferable.
Further, the shape is more preferably approximately spherical or spherical in order to improve the filling property.

When the average particle size is less than 0.3 mm, the retention of the foaming agent is lowered, and it is difficult to reduce the density, which is not preferable. If it exceeds 3.0 mm, not only is the filling property worsened, but it is also difficult to make the foamed molded product thinner, which is not preferable.
In particular, the present invention provides modified resin particles and expandable particles in which a styrenic resin is dispersed in a specific size in a polyethylene resin in the cross section of each particle as described below. be able to.

  That is, each of the particles is a modified resin particle in which a styrene resin is dispersed in a polyethylene resin in a surface layer portion at least 5 μm from the surface and a center portion from the center to a radius of 5 μm. And expandable particles. Here, the particulate styrene resin becomes a continuous phase as shown in the cross-sectional photographs of the central part of Comparative Example 1 and Comparative Example 9, and as a result, when the particle diameter exceeds 0.8 μm, the impact resistance It is not preferable because no significant improvement is observed. In addition, the styrene resin has a state of being dispersed in the form of particles having a particle size of 0.8 μm or less, preferably 0.6 μm or less, in the polyethylene resin. The lower limit of the particle size of the particulate styrene resin (hereinafter referred to as styrene resin particles) is about 0.01 μm. In this way, the styrene resin can be dispersed in a particle state in the surface layer portion and the center portion of the particles.

  The particle size of the styrene resin particles in the surface layer of each particle is preferably 0.01 to 0.8 μm, more preferably 0.01 to 0.6 μm, and still more preferably 0.03 to 0.4 μm. It is. On the other hand, the particle size of the styrenic resin particles at the center of each particle is 0.01 to 0.8 μm, more preferably 0.01 to 0.6 μm, and still more preferably 0.05 to 0.55 μm. It is.

Next, a method for producing modified resin particles and expandable particles will be described.
First, in an aqueous suspension containing a dispersant, 100 parts by weight of polyethylene resin particles, 50 to 800 parts by weight of styrene monomer, and 0.1 to 0.9 parts by weight per 100 parts by weight of the styrene monomer. Disperse the polymerization initiator. In addition, you may mix a styrene-type monomer and a polymerization initiator previously.
Examples of the aqueous medium constituting the aqueous suspension include water and a mixed medium of water and a water-soluble solvent (for example, lower alcohol).

  The dispersant is not particularly limited, and any known dispersant can be used. Specific examples include hardly soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate, magnesium oxide. Further, a surfactant such as sodium dodecylbenzenesulfonate may be used.

  The polyethylene resin particles can be obtained by a known method. For example, a polyethylene-based resin and an inorganic nucleating agent, together with additives as necessary, are melt-kneaded in an extruder and extruded to obtain a strand. The obtained strand is cut in air and cut in water. The method of granulating by cutting while heating is mentioned.

  The polyethylene resin particles have a cylindrical shape, a substantially spherical shape or a spherical shape having an L / D of 0.6 to 1.6 when the length of the particle is L and the average diameter is D, and the average particle size is 0.00. It is preferable that it is 2-1.5 mm. When L / D is smaller than 0.6 or larger than 1.6, that is, the flatness is large, when pre-foamed as styrene-modified foamable particles and filled into a mold to obtain a foamed molded product, It is not preferable because the filling property into the mold tends to deteriorate. Further, the shape is more preferably approximately spherical or spherical in order to improve the filling property. When the average particle size is less than 0.2 mm, the retention of the foaming agent is lowered, and it is difficult to reduce the density, which is not preferable. When it exceeds 1.5 mm, not only is the filling property worsened, but it is also difficult to make the foamed molded product thinner, which is not preferable.

  As the polymerization initiator, those generally used as an initiator for suspension polymerization of a styrene monomer can be used. For example, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxy-3,5 , 5-trimethylhexanoate, t-butyl-peroxy-2-ethylhexyl carbonate, and other organic peroxides. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator used is preferably 0.1 to 0.9 parts by weight and more preferably 0.2 to 0.8 parts by weight per 100 parts by weight of the styrene monomer. If it is less than 0.1 part by weight, it takes too much time to polymerize the styrene monomer, which is not preferable. Use of a polymerization initiator in excess of 0.9 parts by weight is not preferable because the molecular weight of the styrene-based resin is lowered and impact resistance is lowered.

In order to obtain good physical properties, the molecular weight of the styrenic resin is preferably about 200,000 to 500,000, but if the amount of the polymerization initiator used exceeds 0.9 parts by weight, only less than this may be obtained. is there.
The styrene monomer is added in an amount of 50 to 800 parts by weight per 100 parts by weight of the polyethylene resin particles, preferably dispersed under stirring, and the resulting dispersion is heated to a temperature at which the styrene monomer is not substantially polymerized. Then, impregnating the polyethylene resin particles with the styrene monomer.

  In order to sufficiently impregnate the styrene monomer inside the polyethylene resin particles, 30 minutes to 3 hours is appropriate. It is desirable to prevent the formation of a polymer powder of a styrenic resin when the polymerization proceeds before being sufficiently impregnated. The higher the temperature at which the monomer is not substantially polymerized, the more advantageous is the speed of impregnation. However, the temperature must be determined in consideration of the decomposition temperature of the polymerization initiator.

  Next, when the crystallization peak temperature of the polyethylene resin particles is T ° C., the styrene monomer is polymerized at a temperature of (T + 10) to (T + 35) ° C.

  When the polymerization temperature is less than (T + 10) ° C., the styrene resin cannot be dispersed in the form of particles in the vicinity of the center of the modified resin particles, which is not preferable. Furthermore, a temperature exceeding (T + 35) ° C. is not preferable because aggregated particles in which particles are coalesced are generated.

  The modified resin particles can be obtained by the above process. Further, the expandable particles can be obtained by impregnating the modified resin particles during the polymerization or after the polymerization with a volatile foaming agent. This impregnation can be performed by a method known per se. For example, the impregnation during the polymerization can be performed by performing the polymerization reaction in a sealed container and press-fitting a volatile foaming agent into the container. Impregnation after completion of the polymerization is performed by press-fitting a volatile foaming agent in a sealed container.

Modified resin particles and expandable particles having good characteristics can be obtained by the above method, but when the styrene monomer exceeds 100 parts by weight with respect to 100 parts by weight of the polyethylene resin particles, the polymer powder of the styrene resin is large. Tend to be.
In other words, in the above method, when the amount of the styrene monomer relative to 100 parts by weight of the polyethylene resin particles is 50 to 300 parts by weight, the generation of the polymer powder of the styrene resin is small, and the most stable and good characteristics are obtained. Modified resin particles and expandable particles can be easily obtained.

When the styrene monomer exceeds 300 parts by weight, it is preferable to impregnate the polyethylene resin particles in two stages as follows in order to reduce the generation of polymer powder.
First, in an aqueous suspension containing a dispersant, 100 parts by weight of polyethylene resin particles, 30 to 300 parts by weight of styrene monomer, and 0.1 to 0.9 weight with respect to 100 parts by weight of styrene monomer. Part of the polymerization initiator is dispersed. A styrene monomer and a polymerization initiator may be mixed in advance.

Next, the obtained dispersion is heated to a temperature at which the styrene monomer is not substantially polymerized to impregnate the polyethylene resin particles with the styrene monomer.
Furthermore, when the crystallization peak temperature of the polyethylene resin particles is T ° C., the first polymerization of the styrene monomer is performed at a temperature of (T + 10) to (T + 35) ° C.

  Next, a styrene monomer and 0.1 to 0.9 parts by weight of a polymerization initiator per 100 parts by weight of the styrene monomer are added to the reaction liquid for the first polymerization, and the low density polyethylene resin particles are crystallized. When the peak temperature is T ° C., the low-density polyethylene resin particles are impregnated with the styrene monomer and the second polymerization is performed at a temperature of (T + 10) to (T + 35) ° C. However, the total amount of styrene monomers used in the first polymerization and the second polymerization is 50 to 800 parts by weight with respect to 100 parts by weight of the polyethylene resin particles. A styrene monomer and a polymerization initiator may be mixed in advance.

  The second addition of the styrenic monomer and the polymerization initiator may be continuous or intermittent. However, in order to more effectively prevent the formation of the polymer powder, the impregnation and polymerization inside the polyethylene resin particles are almost performed. It is preferable to carry out simultaneously. Since the polymerization is performed at a relatively high temperature, if the addition rate is too high, the polymerization proceeds before impregnation, which is not preferable. For example, the addition rate is preferably 30 to 100 parts by weight / hour.

The modified resin particles can be obtained by the above process. In addition, the expandable particles can be obtained by impregnating resin particles during polymerization or after completion of polymerization with a volatile foaming agent in the same manner as described above. This impregnation can be carried out by a method known per se as described in the Examples.
Furthermore, expandable particles can be made into pre-expanded particles by pre-expanding to a predetermined bulk density (for example, 10 to 300 kg / m ³ , more preferably 10 to 60 kg / m ³ ) by a known method. The method for measuring the bulk density is described in the Examples.

  Further, pre-expanded particles are filled in a mold of a foam molding machine, and heated again to foam the pre-expanded particles, and the foamed particles are heat-sealed to form a foam having a porosity of 5 to 50%. A molded body can be obtained. When the porosity is less than 5%, the foamed molded article does not have sufficient sound absorption. On the other hand, if it is larger than 50%, the bending strength is insufficient, and sound absorption is not obtained because sound waves pass. A preferable porosity is in the range of 5 to 30%.

  The foam molding machine is not particularly limited, and any known foam molding machine can be used. FIG. 12 shows an example of a foam molding machine. This foam molding machine has a female mold 2 and a male mold 3, and the cavities 1 a are formed by combining both the molds 2 and 3. The molds 2 and 3 have steam chambers 2a and 3a, respectively, and are provided with a plurality of steam ejection slit holes 2b and 3b communicating with the steam chambers 2a and 3a and the cavity 1a, respectively. . On the other hand, steam supply pipes 2c and 3c for supplying steam to the respective steam chambers 2a and 3a and steam discharge pipes 2d and 3d for discharging the steam are arranged. A steam controller 4 is disposed in each of the steam supply pipes 2c and 3c, and a drain valve 5 is disposed in each of the steam discharge pipes 2d and 3d.

  Further, the female die 2 is provided with a filling device 7 for filling the pre-expanded particles 6 in the cavity 1a, and in addition, a pressure detection device for detecting the foaming pressure of the pre-expanded particles 6 in the cavity 1a. 9 is installed. And the control means 10 which controls the pressure detection apparatus 9, each steam controller 4, drain valve 5, etc. is provided.

The foam molding method using pre-expanded particles can be roughly divided into a heating step and a cooling step. The heating step is usually (1) mold heating step, (2) one heating step, and (3) reverse one heating. Step (4) In many cases, it is carried out in a subdivided manner, such as a double-sided heating step. An example will be described with reference to FIG.
(1) In the mold heating step, the molds 2 and 3 are mainly heated. Specifically, after the pre-expanded particles 6 are filled in the cavity 1a between the molds by the filler 7, the steam supply pipes are respectively connected to the steam chambers 2a and 3a of both the female mold 2 and the male mold 3. Steam is introduced from 2c and 3c, and air existing in the steam chamber is discharged from the drain valve 5 provided in each of the steam discharge pipes 2d and 3d.
(2) The one heating step is performed for the purpose of preheating for re-foaming the pre-expanded particles 6 or eliminating air in the cavity 1a. This is a step of flowing from the vapor chamber 3a into the gap between the pre-expanded particles 6 filled in the cavity 1a and discharging it out of the system through the vapor chamber 2a of the other mold (female mold 2). Usually, the end point of this process is the time when the pressure of the introduced steam becomes equal to the foaming pressure in the cavity.
(3) The reverse one-side heating step is a step for equilibrating the temperature gradient of the pre-expanded particles 6 generated by the previous one-side heating step, and the steam is discharged from the vapor chamber 2a of the female mold 2 through the reverse route. The pre-expanded particles 6 are introduced into 1 a and heated, and the steam is discharged from the steam chamber 3 a side of the male mold 3.
(4) The double-sided heating process is a process in which the pre-expanded particles 6 are secondarily expanded and finally the expanded particles are fused, and steam is fed into the steam chambers 2a and 3a of both molds 2 and 3. This is done by boosting.
If the molding is carried out along the heating steps (1) to (4), a foamed molded article in which the foamed particles are fused with each other with no voids between the particles can be obtained. It has voids and is required to leave a space between particles during foam molding. Therefore, it is preferable to perform foam molding by the following method.

(A) The mold heating step can be performed in the same manner as in the normal foam molding method. In addition, it is preferable to perform this process for about 3 to 12 seconds.
(B) On the other hand, the air between expanded particles is excluded by a heating process. In this step, heating is continued until the vapor pressure to be introduced is equal to the foaming pressure in the cavity, and the space between the foamed particles can be appropriately filled by further heating. Therefore, this step is preferably performed for 5 to 25 seconds.

Note that the reverse one-side heating step may be performed in order to balance the temperature gradient of the pre-expanded particles 6 as long as the porosity can be maintained within a predetermined range. Specifically, it is preferable to carry out for about 0 to 1 second. The reverse one heating step may be performed before the one heating step.
(C) Since the double-sided heating has an effect of rapidly filling the space between the expanded particles, the double-sided heating may not be performed, or the double-sided heating may be performed for a short time of 3 seconds or less.

By the molding method as described above, it is possible to strengthen the adhesion between the foamed particles, so that a foamed molded product having voids with improved strength can be obtained.
The obtained foamed molded article is excellent in chemical resistance, tough and excellent in bending strength. Moreover, since it is modified with a styrene resin, the rigidity is high. Furthermore, since it has a specific porosity, it is excellent in heat insulation, light weight and sound absorption.

The foamed molded article of the present invention can be used for various applications, and in particular, can be suitably used for automobile interior materials, energy absorbing materials mounted inside bumpers, heavy-weight packaging materials, and the like.
In particular, in the present invention, since a resin using a metallocene catalyst is used as the polyethylene resin, it is possible to obtain a foamed molded article having a bending strength of 0.3 MPa or more. If the bending strength is 0.3 MPa or more, cracks are not easily generated, and it can be used particularly suitably for an energy absorbing material or the like. More preferably, it is 0.32 MPa or more. In addition, the measuring method of bending strength is described in an Example.

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to this. In addition, the measuring method of the various values in an Example and a comparative example is described below.
(Measurement of crystallization peak temperature of polyethylene resin)
The crystallization peak temperature is measured using a differential scanning calorimeter (DSC) according to JIS K7121. Specifically, resin is set as a measurement sample in a DSC measurement container, heated to 280 ° C. at a heating rate of 10 ° C./min, held at 280 ° C. for 10 minutes, and then released to room temperature (23 ° C.). After cooling, the crystallization peak temperature is measured while raising the temperature again at a rate of 10 ° C./min.
(Measurement of melt flow rate of polyethylene resin)
The melt flow rate is measured in accordance with JIS K7210 at 230 ° C. and 10 kgf load.
(Measurement of density of polyethylene resin)
The density is measured according to JIS K6992-2.

(Molecular weight distribution: Mw / Mn measurement)
Measurement is performed by GPC under the following conditions.
Apparatus: GPC apparatus 150C type manufactured by Nippon Waters Co. Column: TSK GMH-6 manufactured by Tosoh Corporation
Solvent: orthodichlorobenzene (ODCB)
Temperature: 135 ° C
Flow rate: 1 ml / min Injection concentration: 10 mg / 10 ml ODCB (injection volume 500 μl)
A weight average molecular weight Mw and a number average molecular weight Mn converted from a calibration curve using standard polystyrene are obtained, and Mw / Mn is calculated.
(Measurement of bulk density)
Measured according to the method described in JIS K 6911: 1995 “General Test Method for Thermosetting Plastics”. Specifically, the pre-expanded particles are naturally dropped into a graduated cylinder with an apparent density measuring device, the weight thereof is measured, and the following formula is calculated.
Bulk density (kg / m ³ ) = Weight (kg) / Particle volume in graduated cylinder (m ³ )

(Porosity)
The foamed molded body having an apparent bulk volume (V1) is immersed in a graduated cylinder filled with a certain amount of water, the increased volume (V2) at that time is measured, and the porosity is obtained by the following equation.
Porosity = {(V1-V2) / V1} × 100
(Bending strength)
The maximum bending strength is measured according to the method described in JIS K9511: 1999 “Foamed plastic heat insulating material”. That is, using a Tensilon universal testing machine UCT-10T (Orientec Co., Ltd.), the specimen size is 75 × 300 × 15 mm, the compression speed is 10 mm / min, the tip jig is a pressure wedge 10R, and a support base 10R. The distance between fulcrums is measured as 200 mm.
(Sound absorption rate)
The sound absorption coefficient is measured by the method described in JIS A 1405: 1998 “Acoustics—Measurement of sound absorption coefficient and impedance by impedance tube—standing wave ratio method”. That is, the sound absorption coefficient at 1 kHz is measured using a normal incident sound absorption coefficient measuring device TYPE10041 (probe tube microphone) manufactured by Electronic Instruments. The sample is 30 mm thick and is measured in close contact with the back plate of the sample holder.

(chemical resistance)
Three flat rectangular plate-shaped test pieces having a length of 100 mm, a width of 100 mm, and a thickness of 20 mm are cut out from the foamed molded article and left to stand at 23 ° C. and a humidity of 50% for 24 hours. In addition, the following test is performed using the molding surface of a foaming molding.
Next, 1 g of different chemicals (gasoline, kerosene, dibutyl phthalate (DBP)) is uniformly applied to the molding surfaces of the three test pieces, and left for 60 minutes at 23 ° C. and 50% humidity. Then, the chemical | medical agent is wiped off from the molding surface of a test piece, the molding surface of a test piece is visually observed, and it judges based on the following reference | standard.
○: Good No change △: Slightly bad Surface softening ×: Bad Surface depression (shrinkage)

Example 1
LLDPE (trade name “FMRN-063” manufactured by Nippon Unicar Co., Ltd., crystallization peak temperature: 101 ° C., melt flow rate: 1.3 g, synthesized from a non-crosslinked linear low density polyethylene resin using a metallocene catalyst / 10 minutes, density: 0.914 g / cm ³ , molecular weight distribution (Mw / Mn): 2.77), and 100 parts by weight of LLDPE and 0.5 parts by weight of talc were fed to the extruder. The feed was melt-kneaded and granulated by an underwater cutting method to obtain oval (egg-like) polyethylene resin particles. The average weight of the polyethylene resin particles was 0.6 mg.

Next, 0.8 parts by weight of magnesium pyrophosphate (dispersant) and 0.02 parts by weight of sodium dodecylbenzenesulfonate (surfactant) were dispersed in 100 parts by weight of water to obtain a dispersion medium.
A suspension was obtained by dispersing 100.5 parts by weight of the polyethylene resin particles in a dispersion medium.
Furthermore, 0.19 part by weight of dicumyl peroxide as a polymerization initiator was dissolved in 100 parts by weight of styrene monomer in advance.

  After adjusting the temperature of the dispersion of the polyethylene resin particles to 60 ° C. and adding a styrene monomer containing a polymerization initiator over a period of 30 minutes, the mixture is stirred for 1 hour at a temperature of 60 ° C. in the polyethylene resin particles. Was impregnated with styrene monomer.

Next, the temperature of the dispersion was raised to 130 ° C. and held for 2 hours, and the styrene monomer was polymerized in the polyethylene resin particles to obtain modified resin particles.
When the dispersion state of the styrene resin in the obtained modified resin particles was observed with a TEM (transmission electron microscope), 0.04 to 0.00 in the surface layer portion (22500 times) (region from the surface to about 5 μm). The styrene resin was dispersed in the form of particles with a particle size of 0.05 to 0.5 μm in 2 μm and the center (12800 times) (region from the center to a radius of about 5 μm). In addition, the cross-sectional photograph of a surface layer part is shown in FIG. 1, and the cross-sectional photograph of a center part is shown in FIG.

Subsequently, 100 parts by weight of the modified resin particles, 0.15 parts by weight of stearic acid monoglyceride and 0.5 parts by weight of diisobutyl adipate are supplied to a pressure resistant V-type rotary mixer having an internal volume of 1 m ³ and rotated at room temperature. As a volatile blowing agent, 14 parts by weight of butane (n-butane: i-butane = 7: 3) was injected. Thereafter, the temperature was raised to 70 ° C. and held for 4 hours, and then cooled to 25 ° C. to obtain expandable particles. Similarly to the modified resin particles described above, the obtained expandable particles were dispersed in the form of styrene resin in a particle size of 0.04 to 0.2 μm in the surface layer part, and 0.05 to 0.5 μm in the center part. The styrene resin was dispersed in the form of particles with a particle size of.

The obtained expandable particles were immediately prefoamed with water vapor to a bulk density of 30 kg / m ³ to obtain prefoamed particles. Next, the pre-expanded particles are filled in a mold of a foam molding machine, and using steam with a steam pressure of 0.08 MPa, heating time: (1) mold heating for 7 seconds, (2) one heating for 15 seconds, (3) Reverse one-side heating for 0.5 seconds and (4) Double-sided heating for 0.5 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.

The following foam molding machine was used for foam molding.
Molding machine used: ACE-3SP (manufactured by Sekisui Koki Co., Ltd.)
Mold size: 300 × 400 × 30mm
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 2
100.5 parts by weight of polyethylene resin particles obtained in the same manner as in Example 1 were dispersed in the dispersion medium obtained in the same manner as in Example 1.
Further, 0.19 part by weight of dicumyl peroxide as a polymerization initiator was previously dissolved in 66 parts by weight of styrene monomer to obtain a first styrene monomer.
The temperature of the dispersion of polyethylene resin particles is adjusted to 60 ° C., a first styrene monomer containing a polymerization initiator is added in a constant amount over 30 minutes, and then the mixture is stirred for 1 hour at a temperature of 60 ° C. The resin particles were impregnated with the first styrene monomer.

Next, the temperature of the dispersion was raised to 130 ° C. and held for 2 hours, and the first styrene monomer was polymerized (first polymerization) in the polyethylene resin particles.
Subsequently, 0.3 part by weight of dicumyl peroxide as a polymerization initiator was dissolved in 534 parts by weight of styrene monomer to obtain a second styrene monomer, and 80 parts by weight per hour was added to the reaction liquid for the first polymerization. Modified resin particles were obtained by continuously dropping into the reaction liquid for the first polymerization over a period of 8 hours and polymerizing (second polymerization) while impregnating into the polyethylene resin particles.

  When the dispersion state of the styrene resin in the obtained modified resin particles was observed with a TEM, 0.05 to 0.35 μm and a central portion (38600) in the surface layer portion (19300 times) (region from the surface to about 5 μm). (Times) (region from the center to a radius of about 5 μm) with a particle size of 0.06 to 0.4 μm, styrene resin was dispersed in the form of particles. In addition, the cross-sectional photograph of a surface layer part is shown in FIG. 3, and the cross-sectional photograph of a center part is shown in FIG.

  Next, expandable particles were obtained in the same manner as in Example 1. Similarly to the modified resin particles described above, styrene resin particles having a particle diameter of 0.05 to 0.35 μm are dispersed in the surface layer portion, and 0.06 to 0.4 μm particles are formed in the center portion. The diameter of the styrene resin was dispersed in the form of particles.

The obtained expandable particles were immediately prefoamed with water vapor to a bulk density of 30 kg / m ³ to obtain prefoamed particles. Next, it was molded in the same manner as in Example 1 to produce a foam molded article. The same molding machine as in Example 1 was used for molding.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

  In addition, the particle size of the styrene resin particles in the surface layer portion and the central portion was confirmed by the following method. That is, for example, by tracing FIG. 4 so that the particle areas are almost the same as shown in FIG. 5 and measuring the particle size one by one, the particle size range is 0.06 to 0.4 μm. I confirmed that there was.

Example 3
A linear low density polyethylene resin manufactured by Sumitomo Chemical Co., Ltd., trade name “Evolu F-201”, melting point: 117 ° C., crystallization peak temperature: 108 ° C., melt flow rate: 1.5 g / 10 min, density: 0 Modified resin particles were obtained in the same manner as in Example 2 except that 915 g / cm ³ and molecular weight distribution (Mw / Mn): 2.5).

  When the dispersion state of the styrene resin in the obtained modified resin particles was observed with a TEM, it was 0.05 to 0.3 μm in the surface layer portion (region from the surface to about 5 μm) and the central portion (radius about 5 μm from the center). The styrene resin was dispersed in the form of particles with a particle size of 0.1 to 0.5 μm in the region up to.

  Next, expandable particles were obtained in the same manner as in Example 1. Similarly to the modified resin particles described above, the obtained expandable particles were dispersed with styrene resin particles having a particle size of 0.05 to 0.3 μm in the surface layer portion, and 0.1 to 0.5 μm particles in the center portion. The diameter of the styrene resin was dispersed in the form of particles.

The foamable particles were prefoamed in the same manner as in Example 2 to obtain prefoamed particles. Next, the pre-expanded particles are filled in a mold of a molding machine, and using steam with a steam pressure of 0.08 MPa, heating time: (1) mold heating for 7 seconds, (2) one heating for 15 seconds, ( 3) Reverse one-sided heating for 0.5 seconds and (4) Double-sided heating for 2 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.
The obtained foamed molded product was a foamed molded product having voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 4
100 parts by weight of the same linear low-density polyethylene resin as in Example 1, 25 parts by weight of iron oxide particles (Fe ₃ O ₄ ), and 0.5 parts by weight of talc were supplied to the extruder. The feed was melt-kneaded and granulated by an underwater cutting method to obtain oval (egg-like) black colored polyethylene resin particles. The average weight of the iron oxide-containing polyethylene resin particles was 0.7 mg.
Modified resin particles and expandable particles were obtained in the same manner as in Example 2 except that the obtained iron oxide-containing polyethylene-based resin particles were used.

When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM in the same manner as in Example 1, the surface layer portion had styrene resin particles with a particle size of 0.05 to 0.3 μm. The styrene resin was dispersed in the form of particles with a particle size of 0.1 to 0.45 μm in the center.
The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 5
Except for using 3 parts by weight of carbon black particles instead of iron oxide particles, polyethylene resin particles colored oval (egg-like) black were obtained in the same manner as in Example 4. The average weight of the carbon black-containing polyethylene resin particles was 0.6 mg.
Modified resin particles were obtained in the same manner as in Example 1 except that the obtained iron oxide-containing polyethylene-based resin particles were used, and then expandable particles were obtained in the same manner as in Example 1.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM in the same manner as in Example 1, the surface layer portion had styrene resin particles with a particle size of 0.06 to 0.3 μm. The styrene resin was dispersed in the form of particles with a particle size of 0.1 to 0.55 μm in the center.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 6
Modified resin particles and expandable particles were obtained in the same manner as in Example 1 except that 95 parts by weight of the styrene monomer and 5 parts by weight of the α-methylstyrene monomer were used.
When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM, 0.04 to 0.2 μm and the central portion (center) were observed in the surface layer portion (region from the surface to about 5 μm). To a radius of about 5 μm), the styrene resin was dispersed in the form of particles with a particle size of 0.05 to 0.5 μm.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 7
Example 2 except that the amount of the first styrene monomer was 50 parts by weight, the amount of the second styrene monomer was 350 parts by weight, t-butyl peroxybenzoate was used as the polymerization initiator, and the polymerization temperature was 115 ° C. Modified resin particles were obtained in the same manner as in Example 1, and then expandable particles were obtained in the same manner as in Example 1.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed with a TEM, 0.05 to 0.4 μm and a central portion (center) were formed on the surface layer portion (region from the surface to about 5 μm). To a radius of about 5 μm), the styrene resin was dispersed in a particle shape with a particle size of 0.1 to 0.5 μm.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 8
Modified resin particles were obtained in the same manner as in Example 7 except that the inorganic nucleating agent to be added was silica, dicumyl peroxide as a polymerization initiator was used, and the polymerization temperature was 140 ° C. Thus, expandable particles were obtained.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM, 0.03 to 0.3 μm and the central portion (center) in the surface layer portion (region from the surface to about 5 μm). To a radius of about 5 μm), styrene resin was dispersed in the form of particles with a particle size of 0.08 to 0.4 μm.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Next, the pre-expanded particles are filled in a mold of a molding machine, and using steam with a steam pressure of 0.08 MPa, heating time: (1) mold heating for 7 seconds, (2) one heating for 12 seconds, ( 3) Reverse one-sided heating for 0.5 seconds and (4) Double-sided heating for 0.5 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.
The obtained foamed molded product had voids. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 9
Modified resin particles were obtained in the same manner as in Example 2 except that the amount of the first styrene monomer was 120 parts by weight and the amount of the second styrene monomer was 80 parts by weight. Got.

When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed with a TEM, 0.04 to 0.3 μm and the center (center) of the surface layer portion (region from the surface to about 5 μm) were observed. To a radius of about 5 μm), the styrene resin was dispersed in the form of particles with a particle size of 0.05 to 0.5 μm.
Pre-expanded particles obtained by pre-expanding the expandable particles in the same manner as in Example 1 were obtained. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molding was void. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 10
After 50 parts by weight of styrene monomer and 0.19 parts by weight of dicumyl peroxide as a polymerization initiator were polymerized at 135 ° C. (first polymerization), the temperature of the reaction system was lowered to 125 ° C., Next, a second styrene monomer obtained by dissolving 0.30 part by weight of dicumyl peroxide as a polymerization initiator in 350 parts by weight of styrene monomer in the reaction liquid for the first polymerization at a rate of 50 parts by weight per hour. By continuously dropping, modified resin particles were obtained in the same manner as in Example 2 except that the resin particles were polymerized while being impregnated with the second styrene monomer (second polymerization). In the same manner as in Example 1, expandable particles were obtained.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM, 0.03 to 0.3 μm and the central portion (center) in the surface layer portion (region from the surface to about 5 μm). To a radius of about 5 μm), styrene resin was dispersed in the form of particles with a particle size of 0.08 to 0.4 μm.

Pre-expanded particles obtained by pre-expanding the expandable particles in the same manner as in Example 1 were obtained. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molding was void. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Example 11
Modified resin particles were obtained in the same manner as in Example 10, and 14 parts by weight of pentane (n-pentane: isopentane = 80: 20, volume ratio) was added instead of butane as a blowing agent. Subsequently, the temperature in the rotary mixer was raised to 30 ° C. and held for 6 hours, and then cooled to 25 ° C. to obtain expandable particles.

When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM, 0.03 to 0.3 μm and the central portion (center) in the surface layer portion (region from the surface to about 5 μm). To a radius of about 5 μm), styrene resin was dispersed in the form of particles with a particle size of 0.08 to 0.4 μm.
The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
The obtained foamed molding was void. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

Comparative Example 1
As a linear low density polyethylene resin (LLDPE) obtained by a Ziegler-Natta catalyst, trade name “TUF-2032” manufactured by Nippon Unicar Co., Ltd. (crystallization peak temperature: 113 ° C., melt flow rate: 0.9 g / 10) Example 1 except that the polymerization temperature was 119 ° C., and the amount of styrene monomer added was 185 parts by weight, using a minute, density: 0.923 g / cm ³ , molecular weight distribution (Mw / Mn): 4.5). In the same manner, modified resin particles and expandable particles were obtained.

  When the styrene resin dispersion state of the resulting modified resin particles and expandable particles was observed by TEM, 0.05 to 0.15 μm styrene was formed on the surface layer (12800 times) (region from the surface to about 5 μm). The resin was dispersed in the form of particles, but in the central part (12800 times) (region from the center of the particle to a radius of about 5 μm), no dispersion of styrene resin particles was seen, confirming that it was a continuous phase. It was. In addition, the cross-sectional photograph of the surface layer part of the modified resin particle is shown in FIG. 6, and the cross-sectional photograph of the central part is shown in FIG.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
Although it was possible to obtain a foamed molded article having voids, the obtained foamed molded article was inferior in bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 2
Ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) (trade name “NUC-3221” manufactured by Nippon Unicar Co., Ltd., vinyl acetate content: 5% by weight, melting point: 107 ° C., melt flow rate: 0.2 g / 10 Min., Density: 0.92 g / cm ³ ) 100 parts by weight and 0.5 parts by weight of synthetic hydrous silicon dioxide are fed into an extruder, melted and mixed, and granulated by an underwater cutting method to form an oval (egg) EVA resin particles were obtained. The average weight of the EVA resin particles was 0.6 mg.

  Next, 0.8 parts by weight of magnesium pyrophosphate and 0.02 parts by weight of sodium dodecylbenzenesulfonate were dispersed in 100 parts by weight of water to obtain a dispersion medium.

A suspension was obtained by dispersing 100.5 parts by weight of the synthetic hydrous silicon dioxide-containing EVA resin particles in a dispersion medium.
Further, 0.19 part by weight of dicumyl peroxide as a polymerization initiator was previously dissolved in 40 parts by weight of styrene monomer to prepare a first styrene monomer.

The temperature of the aqueous medium containing EVA resin particles was adjusted to 60 ° C., the styrene monomer was added in a fixed amount over 30 minutes, and then stirred for 1 hour to impregnate the first styrene monomer in the EVA resin particles.
Next, the reaction system was heated to 85 ° C. and held for 2 hours, and the first styrene monomer was polymerized (first polymerization) in the EVA resin particles.

  Next, a ratio of 50 parts by weight of a second styrene monomer in which 0.19 parts by weight of dicumyl peroxide as a polymerization initiator was further dissolved in 240 parts by weight of styrene monomer in the reaction liquid for the first polymerization. Then, polymerization (second polymerization) was performed while the EVA resin particles were impregnated with the second styrene monomer.

  When the dispersion state of the styrene resin in the obtained modified resin particles was observed with a TEM (surface layer portion 22500 times, center portion 12800 times), particles exceeding 1 μm were observed in the surface layer portion (region from the surface to about 5 μm). The diameter of the styrene resin was dispersed in the form of particles. In the central part (region from the center to a radius of about 5 μm), the styrene resin was not present in the form of particles and was in a continuous state. A cross-sectional photograph of the surface layer portion is shown in FIG.

  Next, expandable particles were obtained in the same manner as in Example 1. Similarly to the modified resin particles described above, the obtained expandable particles had a styrene resin dispersed in the surface layer with a particle size exceeding 1 μm. Moreover, the styrene resin was not present in the form of particles at the center, and was in a continuous state.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
Although a foamed molded article having voids could be obtained, the obtained foamed molded article was inferior in chemical resistance and bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 3
Modified resin particles and expandable particles were obtained in the same manner as in Example 1 except that the amount of styrene monomer used was 10 parts by weight.
When the styrene resin dispersed in the obtained modified resin particles and expandable particles was observed with a TEM, there was almost no particulate styrene resin in the surface layer (region from the surface to about 5 μm), There was no particulate styrene resin in the center (region from the center to a radius of about 5 μm).

  Next, the obtained expandable particles were immediately supplied to a pre-foaming machine and pre-foamed by introducing steam at a pressure of 0.02 MPa, but hardly foamed to obtain pre-foamed particles capable of foam molding. I couldn't.

Comparative Example 4
Resin particles were obtained in the same manner as in Example 1 except that 1.0 part by weight of the polymerization initiator was used. The obtained resin particles contained a large amount of fine powder other than the modified resin particles. This fine powder was a styrene resin powder. The styrene resin powder is produced by polymerization before the styrene monomer is impregnated into the polyethylene resin. Therefore, the polyethylene resin could not be modified with the target amount of styrene resin. Further, since the fine particles inhibit the foamed particles from fusing together during foam molding, a foam molded product for evaluating physical properties could not be obtained.

Comparative Example 5
In the first polymerization, benzoyl peroxide is used as a polymerization initiator, the polymerization temperature is 90 ° C., and in the second polymerization, dicumyl peroxide is used as a polymerization initiator, and the polymerization temperature is Modified resin particles were obtained in the same manner as in Example 7 except that the temperature was 130 ° C., and then expandable particles were obtained in the same manner as in Example 1.

  When the dispersion state of the styrene resin in the resulting modified resin particles and expandable particles was observed with a TEM, the surface layer portion (region from the surface to about 5 μm) and the center portion (region from the center to a radius of about 5 μm) Then, the styrene resin was dispersed in the form of particles with a particle diameter exceeding 1 μm.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
Although a foamed molded article having voids could be obtained, the obtained foamed molded article was inferior in chemical resistance and bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 6
Modified resin particles and expandable particles were obtained in the same manner as in Example 1 except that benzoyl peroxide as a polymerization initiator was used and the polymerization temperature was 90 ° C.
When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed with a TEM, the surface layer portion (region from the surface to about 5 μm) had a particle size exceeding 1 μm in the form of styrene resin. Was dispersed. In the central portion (region from the center to a radius of about 5 μm), the styrene resin was present in a state where some of the particles were continuous.

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
Although a foamed molded article having voids could be obtained, the obtained foamed molded article was inferior in chemical resistance and bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 7
In the first polymerization, dicumyl peroxide is used as a polymerization initiator, the polymerization temperature is 130 ° C., and in the second polymerization, benzoyl peroxide is used as a polymerization initiator, and the polymerization temperature is Modified resin particles were obtained in the same manner as in Example 7 except that the temperature was 90 ° C., and then expandable particles were obtained in the same manner as in Example 1.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed with a TEM, the surface layer portion (region from the surface to about 5 μm) had a particle size exceeding 1 μm in the form of styrene resin. Was dispersed. Further, styrene resin was continuously present in the central portion (region from the center to a radius of about 5 μm).

The expandable particles were pre-expanded in the same manner as in Example 1 to obtain pre-expanded particles. Subsequently, it molded similarly to Example 1, and manufactured the foaming molding.
Although a foamed molded article having voids could be obtained, the obtained foamed molded article was inferior in chemical resistance and bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 8
Using the modified resin particles obtained in Example 10, expandable particles were produced in the same manner as in Example 1 to obtain pre-expanded particles that were pre-expanded in the same manner as in Example 1. Next, the pre-expanded particles are filled in a mold of a molding machine, and using steam with a steam pressure of 0.08 MPa, heating time: (1) mold heating for 7 seconds, (2) one heating for 15 seconds, ( 3) Reverse one-side heating for 2 seconds and (4) Double-sided heating for 10 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.
Since the obtained foamed molded article had a small porosity, it was inferior in the sound absorption coefficient as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 2.

Comparative Example 9
Modified resin particles were obtained in the same manner as in Example 2 except that 834 parts by weight of the second styrene monomer was continuously added dropwise to the reaction liquid for the first polymerization over 10 hours, and then Example 1 was obtained. In the same manner, expandable particles were obtained.

  When the dispersion state of the styrene resin in the obtained modified resin particles and expandable particles was observed by TEM, the surface layer portion (19300 times) (region from the surface to about 5 μm) was 0.07 to 0.4 μm. Styrene resin was dispersed in the form of particles, but in the center (19300 times) (region from the center to a radius of about 5 μm), the particulate styrene resin became a continuous phase. As a result, the particle size exceeded 0.8 μm. It was. In addition, the cross-sectional photograph of a surface layer part is shown in FIG. 10, and the cross-sectional photograph of a center part is shown in FIG.

The obtained expandable particles were immediately prefoamed with water vapor to a bulk density of 20 kg / m ³ to obtain prefoamed particles. Next, the pre-expanded particles are filled in a mold of a molding machine, and using steam with a steam pressure of 0.08 MPa, heating time: (1) mold heating for 5 seconds, (2) one heating for 12 seconds, ( 3) Reverse one-sided heating for 0.5 seconds and (4) Double-sided heating for 0.5 seconds were sequentially performed, and then water-cooled to take out the foamed molded article.
In addition, the molding machine similar to Example 1 was used for shaping | molding.

  Although it was possible to obtain a foamed molded article having voids, the obtained foamed molded article was inferior in bending strength as compared with that obtained in Example 1. The obtained foamed molded product was measured for porosity, bending strength, sound absorption rate and chemical resistance. The results are shown in Table 1.

In Tables 1 and 2, PE means polyethylene, SM means styrene monomer, and αMSM means α-methylstyrene monomer.
While the invention has been described above, it can be readily modified by many means as well. Such variations do not depart from the spirit and scope of the invention, and all such variations obvious to one skilled in the art are intended to be included within the scope of the claims.
This application relates to Japanese Patent Application No. 2004-275278 filed on Sep. 22, 2004, the disclosure of which is incorporated by reference.

It is a TEM photograph of the surface layer section of the modified resin particle of Example 1 according to the present invention. It is a TEM photograph of the center section of the modification resin particle of Example 1 by the present invention. It is a TEM photograph of the surface layer section of the modified resin particle of Example 2 according to the present invention. It is a TEM photograph of the central section of the modified resin particles of Example 2 according to the present invention. It is the figure which traced the TEM photograph of the said FIG. 4 is a TEM photograph of a cross section of a surface layer portion of a modified resin particle of Comparative Example 1. 4 is a TEM photograph of a cross-section at the center of the modified resin particle of Comparative Example 1. 4 is a TEM photograph of a cross section of a surface layer portion of a modified resin particle of Comparative Example 2. 4 is a TEM photograph of a cross-section at the center of modified resin particles in Comparative Example 2. 10 is a TEM photograph of a cross section of a surface layer portion of a modified resin particle of Comparative Example 9. 10 is a TEM photograph of a cross-section at the center of modified resin particles in Comparative Example 9. It is the schematic of the foam molding machine which can be used for this invention.

Explanation of symbols

1a Cavity 2 Female mold 2a, 3a Steam chamber 2b, 3b Steam ejection slit hole 2c, 3c Steam supply pipe 2d, 3d Steam discharge pipe 3 Male mold 4 Steam controller 5 Drain valve 6 Pre-foamed particle 7 Filler 9 Pressure sensing device 10 control means

Claims (4)

50 to 800 parts by weight of a styrene resin with respect to 100 parts by weight of a non-crosslinked linear low density polyethylene resin that can be obtained by using a metallocene catalyst containing an inorganic nucleating agent , and the particle surface A styrene-modified linear low-density polyethylene system having a styrene-based resin dispersed in the form of particles in a surface layer portion of at least 5 μm and a central portion of the particle center to a radius of 5 μm and a particle size of 0.8 μm or less A foam molded article obtained by pre-foaming expandable particles obtained by impregnating resin particles with a volatile foaming agent and foam-molding the obtained pre-foamed particles, and having a porosity of 5 to 50%. The foamed molded product according to claim 1, wherein the inorganic nucleating agent is contained in an amount of 0.1 to 2 parts by weight with respect to 100 parts by weight of the non-crosslinked linear low-density polyethylene resin. The foaming molding of Claim 1 or 2 used for a motor vehicle interior material, a motor vehicle member, or a building member. The foaming molding of Claim 1 or 2 which has a bending strength of 0.3 Mpa or more.

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